There are many situations where is it desirable to locate buried pipes and other conduits. For example, prior to starting any new construction that involves excavation it is important to locate underground water pipes, sewer pipes, septic tanks, reservoirs, gas lines, fiber optic cable conduits, etc. As used herein the term “buried” refers not only to pipes and conduits below the surface of the ground, but in addition, to objects located inside walls, between floors in multi-story buildings or cast into concrete slabs, etc. If a back hoe or other excavation equipment severs a water main, gas line or a sewer line this can lead to extensive damage and messy cleanups. Serious injury or even death can result from inadvertently piercing a gas line during excavation when the gas is ignited.
Buried objects can be located by sensing an electromagnetic signal emitted by the same. Some buried cables such as power lines are already energized and emit their own long cylindrical electromagnetic field and can be located through a process referred to as “line tracing.” Metal pipes and conduits can be energized with an outside electrical source having a frequency typically in a range of approximately 4 Hz to 500 kHz in order to enable them to be located.
A sonde (also called a transmitter, beacon or duct probe) can also be used to locate buried pipes, conduits, horizontal directional drills and reservoirs. A sonde typically includes a coil of wire wrapped around a ferromagnetic core. The coil is energized at a desired frequency, typically in a range of approximately 4 Hz to 500 kHz. A sonde generates a different electromagnetic field than that produced by an energized line. A typical low frequency sonde does not strongly couple to other objects and thereby produce complex interfering fields that can occur during tracing. Therefore, a sonde can be localized to a single point. To take advantage of this feature, a sonde can be constructed as a self-contained unit that can be flushed down a pipe. Alternatively, a sonde can be coupled to a rugged camera head as part of a video pipe inspection system to thereby enable defects and blockages to be precisely located. An example of a hand-held portable locator that can be used to locate a sonde is disclosed in co-pending U.S. patent application Ser. No. 10/268,641 filed Oct. 9, 2002 of Mark S. Olsson et al. entitled OMNIDIRECTIONAL SONDE AND LINE LOCATOR.
Sondes are sometimes integrated into camera heads in video pipe inspection systems. They can also be attached to sewer snakes, drain cleaners and horizontal drill heads. Sondes are also available that are not attached to any guiding structures or remote power sources, but are flushed down a pipe, for example. These include battery powered float-type sondes that are buoyant and battery powered pill-type sondes which do not float and have an elongate configuration.
Sondes that have heretofore been developed have not had a construction that optimizes both utility and durability.